(a) Field of the Invention
The present invention relates to a liquid crystal display and driving method thereof.
(b) Description of the Related Art
Generally, a liquid crystal display (LCD), which includes two panels with respective polarizers and a liquid crystal layer with dielectric anisotropy disposed therebetween, is a display device that displays desired images by applying electric field to the liquid crystal layer to control the amount of light passing through the panels. The LCD includes a plurality of pixels arranged in a matrix, a plurality of gate lines transmitting gate signals to the pixels and extending in a row direction, and a plurality of data lines transmitting data signals to the pixels and extending in a column direction. Each pixel includes a liquid crystal capacitor and a switching element connected thereto, and the liquid crystal capacitor has a pixel electrode and a reference electrode for generating electric field in cooperation and a liquid crystal layer interposed therebetween. Each switching element is connected to one gate line and one data line to be turned on or turned off in response to the gate signal, thereby transmitting the data signal to the pixel electrode. The magnitude of the electric field applied to the liquid crystal layer depends on the difference between the voltage of a reference signal (hereinafter, referred to as a reference voltage) applied to the reference electrode and the voltage of the data signal (hereinafter, referred to as a data voltage). The reference electrode and the pixel electrode may be formed on the same panel or different panels.
When gate-on voltages are sequentially applied to the gate lines, the switching elements connected thereto are turned on. At the same time, the data lines connected to the turned-on switching elements are applied with appropriate data voltages, which are applied to the respective pixel electrodes in a pixel row via the turned-on switching elements. In this manner, the gate-on voltages are applied to all the gate lines to supply the data voltages to the pixels in all the rows, and such a cycle is called a frame.
Since the liquid crystal material is generally deteriorated in its nature by continuous application of electric field in one direction, it is necessary to frequently change the field direction by inverting polarities of the data voltages relative to the reference voltage.
Several methods of inverting the polarities of data voltages are suggested, for example, dot inversion of inverting the polarities by the pixel unit, line inversion of inverting the polarities by the row unit, etc. The dot inversion has problems of severe flickering phenomenon in a screen with middle gray such as a window end screen in a liquid crystal display monitor of a computer as well as delay of signal flowing along the data lines and decrease of charging ratio in every row due to the opposite polarities of voltages of neighboring pixel rows. Although the N-line inversion has less signal delay and less charging ratio reduction compared with the dot inversion, it still has problems of signal delay and reduction of the charging ratio in every first row among the rows with the same polarity.